Introduction
Die casting plays an important role in the manufacturing industry due to its ability to produce complex shapes with precision and repeatability. However, due to the rapid cooling of the molten metal inside the cavity, dimensional and surface variations can occur due to shrinkage or porosity. Different liquid/gas barrier systems can prevent or reduce such defects in terms of dimensional variations and porosity. Among these strategies, squeeze-off insulation is a common cold-bond technique used in die casting.
Squeeze-off insulation is a cold-bond technique in which the molten metal is enclosed in a narrow channel between two cold die walls, resulting in uniform solidification and decreased shrinkage. The squeeze-off insulation process is relatively simple and efficient, with no preheating of the die required. This process also provides high dimensional accuracy of the final product and reduces surface defects. Moreover, due to the absence of vents and the close connection between die and part, porosity and shrinkage are substantially reduced.
Body
In die casting, two types of liquid/gas barrier systems can be generally applied: permeability-based or barrier-based systems. Squeeze-off insulation could be classified as a barrier-based system. These systems rely on their physical or chemical properties to maintain a boundary between the molten metal and air.
The squeeze-off insulation process involves the injection of molten metal into the die cavity, usually from the top at high pressures. As the cavity begins to fill, the molten metal is surrounded by two die walls that are maintained at a cold temperature. This enclosure of metal in a narrow channel between two cold die walls prevents or minimizes dimensional variations and porosity, thus improving the quality of the final product.
The squeezing action of the molten metal against the two die walls leads to uniform cooling in a controlled manner. This allows for efficient mold filling and cooling alongside very small dimensional variances. Furthermore, because the squeeze-off insulation process involves no vents, the system yields minimal porosity defects, thus drastically improving the part quality. The filled die is allowed to cool sufficiently before being ejected, allowing the metal to reach the desired strength and hardness.
Squeeze-off insulation, however, is not free of drawbacks. The homogeneous cooling of metal in the die cavity produces very hard internal surfaces, thus providing a difficult environment for material removal, especially for complex forms or intricate details. Moreover, the fixing of cores in die casting is relatively difficult due to the squeezing action of molten metal.
Conclusion
Squeeze-off insulation is one of the common cold-bond techniques used in die casting. It involves the injection of molten metal into the die cavity, usually from the top at high pressures and an enclosure of metal between two cold die walls. This isolation of metal from the air allows for uniform cooling, which minimizes dimensional variations and porosity in the final product. This also reduces surface defects by eliminating the need for vents. However, this process also produces hard internal surfaces, making it difficult to remove material, especially for complex forms or intricate details. Despite its drawbacks, squeezing-off insulation provides improved dimensional accuracy of die-casted parts and decreased porosity, thus dramatically improving part quality.
